Some memory devices and products are fabricated from multiple memory units. For example, some memory devices are fabricated by assembling multiple memory dies in a Multi-Chip Package (MCP). Solid State Disks (SSDs), media players and other products sometimes comprise multiple memory units. Hard Disk Drives (HDDs) sometimes comprise multiple individual magnetic disks.
The storage capacities of individual memory units in a given device may differ from one unit to another. For example, U.S. Pat. No. 6,363,008, whose disclosure is incorporated herein by reference, describes a multiple-bit-per-cell memory, which includes multiple memory arrays. The number of bits stored per cell is set separately for each of the memory arrays. Memory arrays that testing proves are accurate when writing, storing, and reading a larger number of bits per cell are set to store more bits per cell, and memory arrays that cannot accurately write, store, or read as many bits per cell are set to store fewer bits per cell.
PCT International Publication WO 2007/132456, whose disclosure is incorporated herein by reference, describes a method for data storage in a memory that includes a plurality of analog memory cells. The method includes estimating respective achievable storage capacities of the analog memory cells. The memory cells are then assigned respective storage configurations defining quantities of data to be stored in the memory cells based on the estimated achievable capacities. The data is stored in the memory cells in accordance with the respective assigned storage configurations. The achievable storage capacities of the analog memory cells are re-estimated after the memory has been installed in a host system and used for storing the data in the host system. The storage configurations are modified responsively to the re-estimated achievable capacities.